A variety of medical and cosmetic treatment methods involve exposure of a defined area of tissue to electromagnetic radiation such as light of various wavelength. The light source can be a non-coherent light source such as a suitable lamp or a coherent light source such as a laser.
The application of lasers for therapeutic or cosmetic skin treatment is known in the art. For example laser radiation is used for facial rejuvenation as disclosed in U.S. Patent Application, titled Laser Facial Rejuvenation, Ser. No. 08/382,918 to Slatkine and Mead filed on Feb. 2, 1995. Another example is the use of laser irradiation for hair removal as disclosed in U.S. Provisional Application Ser. No. 60/008,802 to Slatkine, filed Dec. 18, 1995.
A common feature of many cosmetic and therapeutic tissue treatment methods, including laser irradiation of the skin, is the need to achieve a substantially uniform exposure of the surface of the treated tissue.
Another feature of some of these tissue treatment methods is the need to avoid over-exposure of areas of the treated tissue to the treating radiation. This may be particularly important since the treating light beam is often invisible and does not leave any visible mark on the treated area. For example, when a laser is used for depilating defined skin areas, the operator usually positions a laser light source above the surface of the skin and activates the laser to irradiate a certain predetermined skin area, the operator then advances the laser light source to a new position and activates the laser again to irradiate a new skin area. The operator continues in a similar way until all the area to be treated has been irradiated.
Since the depilating beam does not leave any visible mark on the skin, the operator has to memorize or keep track of the already treated area otherwise he might inadvertently irradiate the same skin area repeatedly, thus causing undesirable over-exposure of the skin. Additionally, it can be difficult to manually control the positioning and activation of the laser light source so as to achieve a uniform irradiation of the skin area without leaving non-irradiated areas or causing undesirable over-exposure of skin areas.